Grass boarding

The most common raw materials for the production of boards are wheat, hemp, rye, oats, barley, reeds, rape, flax and maize. It is generally straw produced from these plants that is used. Decomposed plant fibres in the form of peat can also be compressed into boards. The technical properties of hardboards are similar to those of conventional chipboard. However, they are mainly used internally as a base cladding, although in some cases they are used as external cladding.

Hardboards are produced in a range of thicknesses between 3 and 13 mm and can have tongue-and-groove or lap joint edges. Porous boards with good thermal and acoustic properties are also produced, in thicknesses up to 100 mm. The products are often used in demountable partition wall systems.

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Thatching with eelgrass at Lœs0 (Denmark).

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Thatching with eelgrass at Lœs0 (Denmark).

Many types of straw contain natural resins that can be used to glue the boards together. This includes wheat, hemp, flax and barley. The effect can be stimulated by treating the straw with laccase (see page 178). In most products, however, glue is added. Polyurethane adhesive (PUR) is often added in lighter products while methylene-diphenyl-iso-cyanate (MDI) is often used in high-density boards. High-density flax boards are usually produced without additional glue - instead the fibres are boiled for a few hours before the boards are processed.

Boards made of straw are not particularly resistant to vermin, and when used externally they often have to be impregnated with fungicides. If they are rendered, the problem is considerably reduced. The alkaline properties of the render prevent the growth of mould.

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